Has anyone got any advice regarding frozen insects for Lasius Niger?
I'm looking to start a colony in the spring and I'm researching now about their care.

Ideally I would keep a stock of live feeder insects but realistically that's not going to happen, perhaps when the colony grows larger it might be worthwhile.
In their beginning stages however, I would prefer to have a stock of frozen insects that I can thaw out and feed to them.

Buy wingless fruit flies from the local pet shop or the internet (they're not wingless but have curly wings and can still jump around so cool them down before you take the lid off) and some superworms or small crickets. Spiders work, too.
You can boil them (dip into boiling water for 5-10 seconds to remove pests and parasites) and freeze them.

You should crush larger insects (supermworms, crickets) because your colony will have trouble ripping them apart.

A young colony will only need little food (and almost only honey when they have to larvae) so don't buy too much stuff.

And don't feed live insects to young colonies, they often lack the power to kill them. The risk that ants get injured or killed is too high.

Good to hear that they have accepted the frozen food, I just switched from mealworms to crickets (both live tho) and they seem to like it a lot more because it's more soft I guess so I can advise you to continue getting crickets and other soft skin insects for them

My crematigaster colony started out on both pre-killed and frozen crickets and mealworms. I would cut a jumping leg off and then freeze the rest of the cricket and cut what I needed off as I fed. After her 1st hibernation I bought a little cricket holder, and put 12 small crickets in it with a carrot and\or potato for them to eat. Then I could feed small ones and as they grew I would freeze them. Good luck. Just remember u don't have to buy 100s of food at once.